U.S. patent number 4,434,372 [Application Number 06/340,915] was granted by the patent office on 1984-02-28 for method and apparatus for wide angle beam scanning to internally irradiate hollow objects.
This patent grant is currently assigned to Radiation Dynamics, Inc.. Invention is credited to Marshall Cleland.
United States Patent |
4,434,372 |
Cleland |
February 28, 1984 |
Method and apparatus for wide angle beam scanning to internally
irradiate hollow objects
Abstract
Method and apparatus for wide angle beam scanning to internally
irradiate hollow objects with a beam of charged particles utilizes
a scanning deflection device to scan the beam within the object to
be irradiated through an angle of deflection greater than
90.degree. from the axis along which the beam is received by the
scanning deflection device. The object to be irradiated can be
rotated about the scanning deflection device or the scanning
deflection device can be rotated to circumferentially irradiate the
object, and the object is translated relative to the scanning
deflection device to irradiate an entire object, such as a tube, a
container having a closed end or an object having a toroidal
configuration, such as a pneumatic tire.
Inventors: |
Cleland; Marshall (Huntington
Station, NY) |
Assignee: |
Radiation Dynamics, Inc.
(Melville, NY)
|
Family
ID: |
23335463 |
Appl.
No.: |
06/340,915 |
Filed: |
January 20, 1982 |
Current U.S.
Class: |
250/400;
976/DIG.444 |
Current CPC
Class: |
G21K
5/10 (20130101); G01N 23/185 (20130101); B29C
35/08 (20130101); B29L 2030/00 (20130101); B29C
2035/0877 (20130101); G01N 2223/627 (20130101) |
Current International
Class: |
B29C
35/08 (20060101); G21K 5/10 (20060101); G01N
23/02 (20060101); G01N 23/18 (20060101); G01K
001/08 (); H01J 003/14 () |
Field of
Search: |
;250/400,492.3,398 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Smith; Alfred E.
Assistant Examiner: Hannaher; Constantine
Attorney, Agent or Firm: Rose; Howard L.
Claims
What is claimed is:
1. Wide angle beam scanning apparatus for internally irradiating
hollow objects with a beam of charged particles comprising
particle accelerator means for producing a beam of charged
particles; and
scanning deflection means configured to be disposed within an
object to be irradiated for receiving said beam along a beam axis
and deflecting said beam from said beam axis to scan said beam
through an angle of deflection greater than 90.degree. from said
axis whereby the inner surface of the object can be irradiated with
charged particles.
2. Wide angle beam scanning apparatus as recited in claim 1 wherein
said scanning deflection means is rotatable about said beam
axis.
3. Wide angle beam scanning apparatus as recited in claim 1 and
further comprising fixture means for supporting and rotating an
object to be irradiated.
4. Wide angle beam scanning apparatus as recited in claim 1 and
further comprising fixture means for moving an object to be
irradiated in a direction along said beam axis.
5. Wide angle beam scanning apparatus as recited in claim 1 wherein
said scanning deflection means includes generator means supplying a
drive signal and a beam scanning device operable in response to
said drive signal to deflect said beam from an initial angle of
deflection greater than 90.degree. on one side of said beam axis
through a position in alignment with said axis to an angle of
deflection greater than 90.degree. on the opposite side of said
beam axis.
6. Wide angle beam scanning apparatus as recited in claim 5 wherein
said drive signal has shallow slope portions to cause said beam to
be deflected at an angular rate slower at corner regions of an
object to be irradiated than at sides of an object to be
irradiated.
7. Wide angle beam scanning apparatus as recited in claim 1 wherein
said scanning deflection means includes generator means supplying a
drive signal and a beam scanning device operable in response to
said drive signal, said drive signal causing said beam to be
deflected to scan from an angle relative to said beam axis of from
substantially 45.degree. to substantially 135.degree..
8. Wide angle beam scanning apparatus as recited in claim 1 wherein
said scanning deflection means includes generator means supplying a
drive signal and a beam scanning device operable in response to
said drive signal, said drive signal causing said beam to be
deflected to scan from an angle relative to said axis of
substantially 135.degree. on opposite sides of said axis.
9. Wide angle beam scanning apparatus as recited in claim 1 wherein
said scanning deflection means scans said beam through an angle of
deflection greater than 90.degree. on opposite sides of said
axis.
10. Wide angle beam scanning apparatus as recited in claim 9
wherein the object to be irradiated has a hollow toroidal
configuration and further comprising deflection magnet means for
deflecting said beam to coincide with said beam axis.
11. Wide angle beam scanning apparatus as recited in claim 10 and
further comprising means for rotating said object about a central
axis of rotation thereof.
12. Wide angle beam scanning apparatus as recited in claim 10
wherein said deflection magnet means includes quadrupole magnetic
lenses.
13. Wide angle beam scanning apparatus as recited in claim 11
wherein said deflection magnet means is disposed along said central
axis of rotation.
14. Wide angle beam scanning apparatus as recited in claim 13
wherein said beam is supplied along said central axis of rotation
and said deflection magnet means deflects said beam to coincide
with said beam axis.
15. Wide angle beam scanning apparatus as recited in claim 13
wherein said beam is supplied at an angle to said central axis of
rotation and said deflection magnet means deflects said beam to
coincide with said beam axis.
16. A method of internally irradiating hollow objects with a beam
of charged particles comprising the steps of
disposing a beam scanning deflection device within an object to be
irradiated; and
operating the beam scanning deflection device to scan the beam over
an angle relative to a beam axis along which the beam is received
by the beam scanning deflection device to irradiate a swath of an
object to be irradiated.
17. The method as recited in claim 16 wherein said beam scanning
deflection device operating step includes scanning the beam over an
angle relative to the beam axis greater than 90.degree. on opposite
sides of the beam axis.
18. The method as recited in claim 16 wherein said beam scanning
deflection device operating step includes scanning the beam over an
angle relative to the beam axis greater than 90.degree. and not
coinciding with the beam axis.
19. The method as recited in claim 17 wherein said beam scanning
deflection device operating step includes scanning the beam through
an angle relative to the beam axis of substantially 135.degree. to
substantially 45.degree..
20. The method as recited in claim 18 wherein said beam scanning
deflection device operating step includes scanning the beam on
opposite sides of the beam axis.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the internal irradiation of
hollow objects with a beam of charged particles and, more
particularly, to a method and apparatus for effecting such
irradiation with wide angle beam scanning deflection within the
object to be irradiated.
2. Discussion of the Prior Art
Beams of charged particles are commonly used to irradiate objects
to alter material characteristics of the objects, such as by
cross-linking, polymerizing, curing, sterilizing and the like.
Irradiation of flat or cylindrical objects with a beam of charged
particles, such as electrons, is normally accomplished via external
irradiation. That is, flat sheets or films of plastic, rubber or
similar materials are normally irradiated from one or both sides,
and insulated wire and hollow plastic tubing are normally
irradiated from the outside with charged particles sufficiently
energetic to penetrate entirely through the material of the object.
For this type of external irradiation, conventional techniques of
scanning the beam through a small deflection angle range, up to a
maximum of about .+-.30.degree., are sufficient to achieve uniform
radiation dosage. A problem exists, however, when utilizing
conventional beam scanning devices to externally irradiate hollow
objects, such as pipes, vessels, drums, balls, pneumatic tires and
the like, with charged particles insufficiently energetic to
penetrate the walls or shells of the objects in that the
irradiation is not uniform and complete to achieve the desired
results.
Accordingly, prior art beam scanning devices and techniques have
had the disadvantages of not being effective to uniformly irradiate
hollow objects externally because it is extremely important to
assure uniform and complete irradiation of the entire internal
surface of hollow objects in order to achieve the desired effect,
particularly to cure or vulcanize the inner liner of pneumatic
tires or to vulcanize the inner half of the body or tread of the
tire. Prior art methods and apparatus for scanning beams of charged
particles have had the disadvantages of having too narrow a
scanning angle to permit even and thorough internal irradiation of
hollow objects. U.S. Pat. No. 3,632,398 to Konig and British Pat.
No. 717,549 to Siemens-Reiniger-Werke A.G. are representative of
prior art irradiation of interior cavities.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to
overcome the above mentioned problems and disadvantages of the
prior art by utilizing wide angle beam scanning to internally
irradiate hollow objects with a beam of charged particles.
Another object of the present invention is to scan a beam of
charged particles through an angle of deflection greater than
90.degree. from an axis along which the beam is received by a
scanning deflection device to permit wide angle scanning of the
beam internally of a hollow object.
An additional object of the present invention is to internally
irradiate hollow objects with a beam of charged particles by
scanning the beam to define a plane of irradiation covering a
circumferential swath around the object to be irradiated, and
moving rotationally and translationally the beam scanning device or
the object to evenly and thoroughly irradiate all internal surfaces
of the object.
The present invention has a further object in that a device for
deflecting a beam of charged particles over a wide angle internally
of a hollow object to be irradiated is driven at an angular rate
slower at portions corresponding to corners of the object to be
irradiated to thereby evenly irradiate objects having varying
configurations, such as closed end vessels, tanks and the like.
Some of the advantages of the present invention over the prior art
are that the full inner circumference of a hollow object to be
irradiated can be irradiated by disposing a wide angle beam
scanning device within the object, objects of varying
configurations that cannot be irradiated using conventional,
small-angle beam scanning techniques can be irradiated using wide
angle beam scanning in accordance with the present invention, and
the wide angle beam scanning method and apparatus of the present
invention provides even, uniform internal irradiation.
The present invention is generally characterized in a wide angle
beam scanning apparatus for internally irradiating hollow objects
with a beam of charged particles including a particle accelerator
for producing a beam of charged particles and a scanning deflection
device configured to be disposed within an object to be irradiated
for receiving the beam along beam axis and deflecting the beam from
the beam axis to scan the beam through an angle of deflection
greater than 90.degree. from the axis whereby the inner surface of
the object can be irradiated with charged particles.
The present invention is further generally characterized in method
of internally irradiating hollow objects with a beam of charged
particles including the steps of disposing a beam scanning
deflection device within an object to be irradiated, and operating
the beam scanning deflection device to scan the beam over an angle
relative to a beam axis along which the beam is received by the
beam scanning deflection device to irradiate a swath of an object
to be irradiated.
Other objects and advantages of the present invention will become
apparent from the following description of the preferred embodiment
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of wide angle beam scanning apparatus
in accordance with the present invention for internally irradiating
a hollow object.
FIGS. 2 and 2a illustrate drive signal waveforms for the scanning
deflection device of the apparatus of FIG. 1.
FIG. 3 is a diagrammatic view of a modification of the wide angle
beam scanning apparatus of FIG. 1.
FIG. 4 is a diagrammatic view of the wide angle beam scanning
apparatus of FIG. 3 utilized to irradiate a closed end object.
FIG. 5 illustrates a drive signal waveform for the scanning
deflection device of the apparatus of FIG. 4.
FIG. 6 is a diagrammatic view of an embodiment of the wide angle
beam scanning apparatus of the present invention utilized for
irradiating pneumatic tires.
FIG. 7 is a diagrammatic view of a modification of the apparatus of
FIG. 6.
FIG. 8 is a diagrammatic side view partially in section of another
apparatus for irradiating the interior of a tire carcass.
FIG. 9 is an end view of the apparatus of FIG. 8.
FIG. 10 is a detailed perspective view of the member 20 of FIG.
1.
FIG. 11 is a section along line 11--11 of FIG. 10.
FIG. 12 is a sectional view of the part within the circle
designated FIG. 12 in FIG. 11.
FIG. 13 is a section taken aong line 13--13 of FIG. 12.
FIG. 14 is a detail view in section taken vertical along a plane
through the center of the structure of FIG. 10.
FIG. 15 illustrates the aligning pins located in the cover for
closing the deflection chamber of FIG. 11.
FIG. 16 is a detailed view of the structure for reaching the
chamber of FIG. 15.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Wide angle beam scanning apparatus 10 according to the present
invention is illustrated in FIG. 1 and includes a particle
accelerator 12, such as an electron beam accelerator, as described
in U.S. Pat. No. 2,875,394 to Cleland, supplying a beam of charged
particles via a vacuum pipe 14, a rotating joint 16 and a vacuum
pipe 18 to a beam scanning deflection device 20 having a vacuum
chamber 22 and a beam scanning magnet 24 receiving a drive signal
from a generator 26 to control deflection of a beam of electrons
received by the device 20 along an axis 28. An object to be
irradiated 30, such as a hollow pipe or tube, is supported on a
fixture 32, and the scanning deflection device 20 is rotatable
within the object 30 while the object 30 is translated in a
direction along the axis 28 by fixture 32 such that the length of
the object can be irradiated while the scanning deflection device
is rotated to irradiate a circumferential swath around the
object.
A drive signal 34 for driving the scanning deflection device 20 is
illustrated in FIG. 2 and has a sawtooth or preferably a triangular
waveform such that for each cycle the beam is initially deflected
an angle greater than 90.degree. from the axis 28, preferably an
angle of about 135.degree., and thereafter the beam is scanned
through the axis 28 to terminate at an angle of 135.degree. on the
opposite side of the axis providing a 270.degree. scan. The beam is
then returned to the initial deflection position at the beginning
of the next cycle. Accordingly, the drive signal 34 will scan the
beam while the scanning deflection device 20 is rotated to
irradiate a circumferential swath along the inner surface of the
object 30, and the length of the object 30 is irradiated as the
object is moved along the axis 28 by fixture 32.
A variation of a drive signal for driving scanning deflection
device 20 is shown in FIG. 2a wherein each cycle of the drive
signal 36 has positive and negative ramp portions 38 and 40,
respectively, such that the beam is scanned from an initial
deflection angle of 135.degree. relative to the axis 28 to a
deflection angle of 45.degree. and then scanned from 135.degree. to
45.degree. on the opposite side of axis 28. In this manner, the
irradiated circumferential swath is reduced in width with a
resulting increase in efficiency due to elimination of the portion
of the scan extending along the axis 28 within 45.degree. on either
side thereof.
In the modification of FIG. 3, the object 30 is rotated as well as
longitudinally moved by fixture 32 such that the scanning
deflection device 20 can be held stationary while the object is
simultaneously rotated and translated coaxially along the beam axis
28. The structure of the modification of FIG. 3 is the same as that
of FIG. 1 with the exception that joint 16 is not required and the
vacuum pipe 14 can lead directly to the scanning deflection device
20. The drive signal waveforms of FIGS. 2 or 2a can be used to
drive the scaning deflection device dependent upon the width of the
circumferential irradiated swath desired.
Where the object to be irradiated has a relatively short length
with a closed end, such as a drum-type container 42 as shown in
FIG. 4, the beam scanning apparatus can be the same as that of FIG.
3 with the drive signal for the scanning deflection device 20
having a waveform 44 as shown in FIG. 5 producing a scan pattern
modulated to provide a uniform radiation dosage over the entire
inner surface of the container 42 including the "corner" regions 46
where the end and side walls of the container meet. To this end,
the drive signal waveforms 34 or 36 of FIGS. 2 and 2a can be used
to irradiate the inner surface of the side wall of the container as
the container is translated along axis 28, and the drive signal
waveform 44 is used for irradiation of the corner and end regions
of the container. The drive signal waveform 44 has a general
sawtooth or triangular configuration; however, the ramp 48 of the
waveform is non-linear with shallow slope portions 50 and 52
positioned to cause the beam to dwell at the corner regions to
cause more electrons to be deposited thereat. The shallow slope
portions 50 and 52 distort waveform 44 from a linear or
"triangular" sawtooth waveform and are required because, as the
container rotates about the beam axis 28, the area of the annular
end portions irradiated with electrons will increase in direct
proportion to the displacement from the central axis such that the
dwell time of the beam should increase as the deflection angle from
the beam axis increases. Accordingly, the drive signal generator is
programmed to drive the scanning deflection device to scan a
circumferential swath, such as from 45.degree. to 135.degree. on
opposite sides of the beam axis, and irradiate the cylindrical side
wall during axial movement of the container; and, when the scanning
deflection device has reached the deepest penetration, the drive
signal generator is programmed to produce the drive signal waveform
44 to uniformly irradiate the end corner regions of the container.
If desired, a drive signal waveform can be used to produce a scan
of 0.degree. to 45.degree. on either side of the beam axis to
irradiate the corner and end regions of the container, such a drive
signal waveform having a sawtooth shape.
Wide angle beam scanning apparatus 54 for irradiation of an object
having a toroidal shape, such as a pneumatic tire 56, is shown in
FIG. 6 and includes a vacuum pipe 14 supplying a beam of electrons
58 from an electron beam accelerator (not shown) to a beam
deflection magnet 60 disposed along the central axis of the tire 56
and in a central plane through the tire, the magnet 60 deflecting
the beam 58 by 90.degree. to direct it via a vacuum pipe 64 to the
scanning deflection device 20 along beam axis 28. Quadrupole lenses
62 may be used before and after the 90.degree. deflection magnet to
compensate for the asymetrical focus of the magnet so as to deliver
a small-diameter electron beam to the scanning deflection device
20. The scanning deflection device 20 is disposed within the
carcass of the tire 56, and the tire is supported on a rotating
fixture 66 for rotating the tire about its axis.
In operation, the wide angle beam scanning apparatus 54 can be used
to cure the inner liner of tire 56 by placing the tire on fixture
66 and positioning the tire to have the scanning deflection device
20 disposed therein. The scanning deflection device is desirably
driven with a sawtooth or triangular waveform, such as waveform 34
of FIG. 2, such that the beam 58 received along axis 28 is scanned
from an angle relative to the beam axis of 135.degree. on one side
of the axis to 135.degree. on the opposite side of the axis while
the tire is rotated about its axis by fixture 66. In this manner,
the entire inner liner of the tire is irradiated by the wide angle
beam scanning from scanning deflection device 20 coupled with the
rotation of the tire.
A modification of the wide angle beam scanning apparatus of FIG. 6
is shown in FIG. 7 wherein the electron beam 58 is not supplied
along an axis coinciding with the axis of rotation of the tire but
rather is supplied at approximately an angle of 45.degree. to the
axis of rotation of the tire thereby having the advantage of
requiring only a 45.degree. deflection by a deflection magnet 68
disposed along the axis of rotation of the tire centrally of the
tire. The reduced deflection angle of the deflection magnet coupled
with elongating the pole tips thereof weakens the focal properties
of the deflection magnet which is beneficial in accurately scanning
the beam within the tire and supplying the beam to the scanning
deflection device 20 via vacuum pipe 64. That is, the use of a
90.degree. deflection magnet causes the beam to focus and diverge
before reaching the scanning deflection device which can cause
undesirable beam loss and bombardment of the scanning deflection
device unless compensated by the quadrupole lenses. The 45.degree.
deflection magnet 68 has a much longer focal length thereby
reducing the problems associated with a diverging beam. The drive
signal waveform supplied to the scanning deflection device 20 is
preferably the sawtooth or triangular waveform 34 of FIG. 2 such
that the entire inner liner of the tire is irradiated as the tire
is rotated.
Another embodiment of the scanning apparatus of the present
invention is illustrated in FIGS. 8 and 9 of the accompanying
drawings. In this embodiment, the beam is again directed along the
axis of the line 58 but is rotated 270.degree. in a magnetic
arrangement to be described.
A deflection magnet assembly 70, as illustrated in co-pending
application Ser. No. 063,822 filed on Aug. 6, 1979 in the names of
Thompson, et al. and assigned to the assignee of the present
invention, may also be employed. The assembly includes a pair of
magnetic pole pieces 72 and 74 positioned along opposite sides of a
deflection chamber 76 and electrical windings 78 and 80 are wound
around the pole pieces which are coupled with a magnetic flux
return yoke 82. The magnetic pole pieces 72 and 74 are arranged at
an angle of 45.degree. to the central axis of the electron beam
entering the assembly 70 via pipe 84 and leaving the assembly via
pipe 14.
The assembly is located in an evacuated deflection chamber 86 that
can be made of any non-magnetic metal, such as stainless steel;
and, heavy gauge material can be used in the construction of the
deflection chamber since the deflection field does not have any AC
components. The deflection magnet assembly 70 can be made of solid
iron or steel plates since the magnetic field is constant, the pole
pieces 72 and 74 being preferably flat and arranged in parallel
relation to produce a uniform magnetic field. The edges of the pole
pieces where the scanning electron beam enters the influence of the
magnetic field can be shaped to control the focal properties of the
deflection magnet.
In operation, a focused electron beam is introduced to the
deflection magnet assembly 70; the beam being focused in order to
permit the use of a small gap between the poles 72 and 74 of the
deflection magnet assembly to enhance its efficiency. When the
electrons of the beam enter the field established between pole
pieces 72 and 74, they execute circular orbits to emerge at the
side of the chamber 76 at which the pipe 14 is located. With the
deflection magnet assembly 70 oriented at 45.degree. relative to
the central axis of the electron beam, the electron beam will
execute a turn of substantially 270.degree. to emerge at
substantially a right angle to its original direction. The rays of
the electron beam exit deflection chamber 76 through pipe 14 and
are introduced into the scanning member or device 86 in order to
permit uniform irradiation of the internal surface of the tire 56
which is rotated relative to the deflection chamber for
circumferential irradiation.
The deflection chamber and deflection magnet assembly are arranged
co-axially with the tire 56 and, for use in irradiating other
hollow objects, would similarly be disposed along an axis of
symmetry of the object.
In each of the wide angle scanning apparatuses of the present
invention, the scanning deflection device is disposed within the
hollow object to be irradiated and the object is rotated about the
scanning deflection device or the scanning deflection device is
rotated within the object. Accordingly, the fixtures for supporting
the objects to be irradiated are desirably designed to pick up the
object to be irradiated, rotate the object about a central axis
thereof and translate the rotating object by the scanning
deflection device such that the scanning deflection device is
disposed within the object. The fixture for supporting tires for
irradiation by the scanning deflection device also will tilt the
tire for proper positioning relative to the scanning deflection
device assuming that the initial direction of the electron beam is
either horizontal or vertical.
The scanning of the beam is desirably accomplished in a single
plane to avoid striking the pole tips or coils of the scanning
deflection device magnet, and the exact shape of the drive signal
waveforms will depend on the configuration of the scanning
deflection device magnet and the angular deflection scan range
required for irradiating various regions of objects to be
irradiated. The annular deflection scan range will vary with
various applications, and the deflection scan can be produced on
one or both sides of the beam axis.
Referring now specifically to FIGS. 10 to 16, there is illustrated
in detail the construction of the beam scanning deflection device
20. The device 20 comprises, and reference is made initially to
FIG. 10, a hollow, flat deflection chamber 90 and magnet assembly
92.
The deflection chamber 90 comprises two flat circular discs 94 and
96 having spacing ribs 98 disposed between and equally spaced about
the outer periphery only of the discs 94 and 96 for support; the
ribs being bonded in place by suitable means such as welding. The
ribs must withstand only compression forces of atmospheric pressure
and thus tacking of the ribs should be sufficient.
An arcuate metal plate 100 is suitably secured (for example by
braising) between the discs at their outer peripheries supplying
the support between the discs 94 and 96 over a short arcuate
region. The plate 100 receives the end of the vacuum pipe 14 in
aperture 102 therein.
The space between the discs 94 and 96 is sealed by a foil window
109 which extends from one side of pipe 14 about the outer
periphery of the edges of discs 94 and 96 to the other side of the
pipe 14. The foil window is clamped against the edges of the discs
by suitable clamps in the nature of pipe or hose clamps, pipe
clamps 104 and 106 being illustrated in FIG. 10. In order to assure
a proper seal, soft aluminum wire 107 is placed in a shallow groove
108 extending around the outer periphery of the edge of each of the
discs 94 and 96 and lies between the foil and the discs. When the
clamps 104 and 106 are drawn tight, the aluminum wire is mashed and
seals the interface between the foil and the edges of the discs.
Clamping bars 120 hold the foil against the wire 107 (see FIG. 16)
where it comes over plate 100. Bars 120 are bolted to member
100.
The discs 94 and 96 should be fabricated of a strong material
having a high electrical resistivity to reduce eddy current losses.
Inconel is a suitable material and may be employed for the plate
100 also. The foil is preferably of titanium.
Referring now to the magnetic structure 92, flat circular discs 110
and 112 of high permeability magnetic material such as ferrite are
disposed against the outer surfaces of the discs 94 and 96. Annular
electric coils 114 and 116 are disposed about the circular edges of
discs 110 and 112 and are excited by the generator 26 to establish
a varying field extending across the chamber 20 whereby to cause
the beam to sweep sequentially and successively from one end of
foil window 109 to the other end thereof; approximately
270.degree..
A yoke 118 of magnetic material, such as ferrite, is employed to
complete the magnetic path to provide a low external field. A large
external field would produce some reverse bending of the electron
beam and reduce its angular deflection.
The yoke 118 has two large faces 120 that are coextensive with
discs 110 and 112 and coils 114 and 116. The faces are joined by a
cross member 122 that extends transverse of the plane of the faces
120 and is apertured to accept the pipe 14.
Inasmuch as the present invention is subject to many variations,
modifications and changes in detail, it is intended that all
subject matter described above or shown in the accompanying
drawings be interpreted as illustrative and not in a limiting
sense.
* * * * *